Refractory products of oxide-carbon mixtures are known in different forms. In the so-called tar-dolomite and tar-magnesium bricks, a mixture of calcined dolomite, calcined magnesite or sintered magnesia is bound with tar or pitch. The binding tar or the binding pitch is converted to binding coke by tempering, or low temperature treatment below coking and increased heating of the lined vessels. Heat and cold-curable synthetic resins with relatively high coke yield are also used as binding agents for this purpose in place of the tar and pitch. To increase the slag resistance, fine graphite and coke powder are additionally added to such bricks up to approximately 20 percent by weight. Oxides other than those mentioned above can serve as basic materials in the manufacture of carbon-bound oxide bricks, including sintered aluminum oxide, sintered zirconium oxide or sintered mullite (chemical formula 3Al.sub.2 O.sub.3. 2SiO.sub.2).
Another group of refractory products which is known in the art are the ceramic-bound refractory bricks, which contain in addition to the materials identified above, carbon or natural graphite. The clay-graphite substances (also known as plumbago) are primarily used in the manufacture of melting crucibles and are a known example of this group.
With respect to carbon bricks it has proven desirable for some applications, such as those in which the brick must come into contact with pig iron, to add fine-particle oxides, in particular aluminum oxide, in quantities of up to approximately 10 percent by weight.
The resistance to gaseous and liquid substances of an oxide-carbon combination brick is not solely a function of the oxide/carbon ratio in the mixture and the individual resistance of its components, but also of the manner in which they are mixed and fabricated. In the manufacture of large-sized refractory blocks, it must further be taken into consideration that for this purpose, coarser grain fractions are required.
It is an object of the present invention to mix and bind oxides and carbon in such a way, that, on the one hand, optimum resistance against gaseous and liquid media in the metallurgical units is ensured and, on the other hand, large-sized refractory bricks can be manufactured.
A further object of the present invention is to achieve through the nature of the oxide, the additives, and the pitchbinder as well as through thermal treatment in the baking or calcining furnace, maximum strength and density of the fired intermediary product.
These and other objects of the present invention will be apparent to those of ordinary skill in the art in light of the following description and accompanying claims.